I was at home (a block away) when the Adelphi came down in February of 2006. I remember walking over to watch. They always demolish these buildings from the back. There are probably structural and safety reasons for this, but it also means that once the demolition is noticeable it's almost complete.
Early modernists claimed to prefer the backs of buildings rather than the ornamental front facades, since that was supposedly where the true structure was expressed. What you see here would likely please any number of architectural theorists from the 50s and 60s.
It is fascinating to see how these buildings developed over the years. I've tried to make them visually intelligible, but it's a tricky job.
If a building is only visible from a street the architect can focus the design (and dollars) on the front facade. Once something is demolished it reveals the areas intended to remain hidden. If it happens enough it changes the entire feel of a block, making it look slapped together, run-down and ready for the bulldozer. It may be all of those things, but usually what you're seeing is just the architectural vocabulary for functional spaces.
In the foreground is the foundation of a new condo building which was intended to replace the Adelphi Theater. The development stalled in the economic downturn and has remained vacant ever since.